The present invention relates to composite elements which have the following layer structure:
(i) from 2 to 20 mm, preferably from 5 to 20 mm, particularly preferably from 5 to 10 mm, of metal,
(ii) from 10 to 300 mm, preferably from 10 to 100 mm, of polyisocyanate polyaddition products obtainable by reacting (a) isocyanates with (b) compounds which are reactive toward isocyanates in the presence of from 0.1 to 50% by volume, preferably from 1 to 20% by volume, based on the volume of the polyisocyanate polyaddition products, of at least one gas (c) and also, if desired, (d) catalysts. and/or (e) auxiliaries and/or additives,
(iii) from 2 to 20 mm, preferably from 5 to 20 mm, particularly preferably from 5 to 10 mm, of metal.
The invention further relates to a process for producing these composite elements and to their use.
The construction of ships, for example ship""s hulls and hold covers, bridges or high-rise buildings require the use of structural components which can withstand considerable external forces. Owing to these requirements, such structural components usually comprise metal plates or metal supports which are strengthened by means of an appropriate geometry or suitable struts. Thus, hulls of tankers usually consist, because of increased safety standards, of an inner and an outer hull, with each hull being made up of 15 mm thick steel plates which are connected to one another by steel struts about 2 m long. Since these steel plates are subjected to considerable forces, both the inner and outer steel shells are reinforced by welded-on reinforcing elements. Disadvantages of these classical structural components are both the considerable amounts of steel which are required and the time-consuming and labor-intensive method of manufacture. In addition, such structural components have a considerable weight resulting in a lower tonnage of the ship and increased fuel consumption. Furthermore, such classical structural elements based on steel require a great deal of maintenance since both the outer surface and the surfaces of the steel parts between the outer and inner shells regularly have to be protected against corrosion.
It is an object of the present invention to develop structural components which withstand high external forces and can be used, for example, in shipbuilding, bridge construction or construction of high-rise buildings. The structural components to be developed, also referred to as composite elements, should be able to serve as replacements for known steel structures and, in particular, have advantages in respect of their weight, manufacturing process and maintenance intensity. In particular, the composite elements having large dimensions should be simple and quick to produce and also be able to be used in shipbuilding due to an improved resistance to hydrolysis.
We have found that this object is achieved by the composite elements described at the outset.
The composite elements of the present invention have, apart from excellent mechanical properties, the particular advantage that composite elements having very large dimensions are also obtainable. Such composite elements, which are obtainable by preparing a synthetic polymer (ii) between two metal plates (i) and (iii), have hitherto been obtainable only to a restricted extent because of the shrinkage of the synthetic polymer (ii) during and after its reaction. Owing to the shrinkage of the synthetic polymer (ii), for example the polyisocyanate polyaddition products, partial detachment of the synthetic polymer (ii) from the metal plates (i) and/or (iii) occurs. However, a very complete and very good adhesion of the synthetic polymer (ii) to the metal plates (i) and/or (iii) is of particular importance to the mechanical properties of such a composite element. The reaction of (a) with (b) in the presence of (c) largely avoids the shrinkage of (ii) and thus partial detachment from (i) and/or (iii).
As component (c) for preparing (ii), it is possible to use generally known compounds which are preferably gaseous at 25xc2x0 C. and a pressure of 1 bar, for example air, carbon dioxide, nitrogen, helium and/or neon. Preference is given to using air. The component (c) is preferably inert toward the component (a), particularly preferably toward the components (a) and (b), i.e. reaction of the gas with (a) and (b) is barely detectable, preferably undetectable. The use of the gas (c) is fundamentally different from the use of customary blowing agents for producing foamed polyurethanes. While customary blowing agents are used in liquid form and during the reaction either vaporized as a result of the heat of reaction or else, in the case of water, form gaseous carbon dioxide owing to the reaction with the isocyanate groups, in the present invention preference is given to using the component (c) in gaseous form.
For preparing (ii), preference is given to using, as (e), customary foam stabilizers which are commercially available and are generally known to those skilled in the art, for example generally known polysiloxane-polyoxyalkylene block copolymers, e.g. Tegostab 2219 from Goldschmidt. The proportion of these foam stabilizers in the preparation of (ii) is preferably from 0.001 to 10% by weight, particularly preferably from 0.01 to 10% by weight, in particular from 0.01 to 2% by weight, based on the weight of the components (b), (e) and, if used, (d) employed for the preparation of (ii). The use of these foam stabilizers stabilizes the component (c) in the reaction mixture for preparing (ii).
The composite elements of the present invention can be produced by preparing, between (i) and (iii), polyisocyanate polyaddition products (ii), usually polyurethanes which can, if desired, contain urea and/or isocyanurate structures, which adhere to (i) and (iii) by reacting (a) isocyanates with (b) compounds which are reactive toward isocyanates in the presence of from 1 to 50% by volume, based on the volume of the polyisocyanate polyaddition products, of at least one gas (c) and also, if desired, (d) catalysts and/or (e) auxiliaries and/or additives.
The polyisocyanate polyaddition products can be described as compact products despite the use of (c), since a network of gas-filled cells is not formed.
The reaction is preferably carried out in a closed mold, i.e. (i) and (iii) are present, during filling with the starting components for preparing (ii), in a mold which is closed after complete introduction of the starting components. After the reaction of the starting components for preparing (ii), the composite element can be removed from the mold.
The surfaces of (i) and/or (iii) to which (ii) adheres after production of the composite elements are preferably sandblasted. This sandblasting can be carried out by conventional methods. For example, the surfaces can be blasted with customary sand under high pressure and thus, for example, cleaned and roughened. Suitable equipment for such treatment is commercially available.
This treatment of the surfaces of (i) and (iii) which are in contact with (ii) after the reaction of (a) with (b) in the presence of (c) and also, if desired, (d) and/or (e) leads to considerably improved adhesion of (ii) to (i) and (iii). Sandblasting is preferably carried out immediately before introduction of the components for preparing (ii) into the space between (i) and (iii).
The sandblasted metal plates may, if desired, be pretreated with primers customary in the shipbuilding industry. Such products are usually based on alkyl silicates or are primers having a high zinc content and based on epoxides or polyurethanes, and may be tar-modified.
After the preferred treatment of the surfaces of (i) and (iii), these layers are preferably fixed in a suitable arrangement, for example parallel to one another. The spacing is usually selected such that the space between (i) and (iii) has a thickness of from 10 to 300 mm, preferably from 10 to 100 mm. (i) and (iii) can, for example, be fixed in place by means of spacers. The edges of the intermediate space are preferably sealed such that the space between (i) and (iii) can be filled with (a) and (b) and (c) and also, if desired, (d) and/or (e) but these components are prevented from flowing out. Sealing can be carried out using customary plastic films or metal foils and/or metal plates which can also serve as spacers.
The layers (i) and (iii) are preferably customary metal plates, for example steel plates, having the thicknesses according to the present invention.
The space between (i) and (iii) can be filled either with (i) and (iii) aligned vertically or with (i) and (iii) aligned horizontally.
The filling of the space between (i) and (iii) with (a), (b) and (c) and also, if desired, (d) and/or (e) can be carried out using customary feeding equipment, preferably continuously, for example by means of high- and low-pressure machines, preferably high-pressure machines.
The feed rate can be varied depending on the volume to be filled. To ensure homogeneous curing of (ii), the feed rate and the feeding equipment are selected such that the space to be filled can be filled with the components for preparing (ii) within 0.5-20 minutes.
As layers (i) and (iii), usually plates, use can be made of customary metals, for example iron, conventional steel, all types of alloy steel, aluminum and/or copper.
Both (i) and (iii) can be used in coated form, for example primed, painted and/or coated with customary plastics, for producing the composite elements of the present invention, for example coated with the abovementioned primers. Preferably, (i) and (iii) are used in uncoated form and are particularly preferably cleaned, for example by customary sandblasting, before use.
The preparation of the polyisocyanate polyaddition products (ii), usually polyurethane and if desired polyisocyanurate products, in particular polyurethane elastomers, by reacting (a) isocyanates with (b) compounds which are reactive toward isocyanates in the presence of (c) and also, if desired, (d) catalysts and/or (e) auxiliaries and/or additives has been described extensively. The addition of blowing agents to the starting components for preparing (ii) is preferably avoided. To very largely avoid an uncontrolled foaming process, both the starting components (b) and (c) and also, if used, (d) and/or (e) as well as the surfaces of (i) and (iii) which come into contact with the reaction components should preferably be dry.
The water content of the reaction mixture comprising (a), (b), (c) and, if used, (d) and/or (e) is preferably from 0 to 0.3% by weight, particularly preferably from 0 to 0.03% by weight, in particular 0% by weight, based on the weight of the reaction mixture. The water content of, in particular, the component (b) can be set to the appropriate level by, for example, distillation. It is also possible to add compounds which bind water and thus prevent a blowing reaction to the reaction mixture. Such compounds, for example molecular sieves, are generally known. For example, it is possible to use silicates and oxazolidines in a suitable, preferably finely divided form. These compounds are preferably added to the reaction mixture, preferably the component (b), in amounts of from 0 to 5% by weight, particularly preferably from 1 to 3% by weight, based on the weight of the reaction mixture.